Wind energy conversion
Fun project. Get a fan and do some model work with some balsa impellors.
Design the body shape to have a minimum drag, perhaps knowing the fan rotation you could take advantage of body shape and get a sail boat effect.
Does the impeller have to be a fan shape or could you use a vertically rotating cylinder?
You could get torque and possibly a favorable lift vector. There is a vertical configuration that looks like a old combine front rake assembly that is used in wind generators. With proper adjustment of individual wings as it rotates you could maximize the torque by having full flat (or optiimum angle of attack) on the going aft power segment of the rotation and zero incidence on the forward going segment.
Minimize weight, drag and friction and have just enough traction with ground to overcome the aero and friction drags.